1. Field of the Invention
The present invention relates to devices and methods for injection of a viscous material into a living subject. This invention particularly relates to devices and methods for filling bone voids. This invention more particularly relates to height restoration of a bone, for example, for treating Vertebral Compression Fractures (VCFs).
2. Description of the Related Art
A common occurrence in older persons is compression fractures of the vertebrae. This causes pain and a shortening (or other distortion) of stature. One common treatment is vertebroplasty, in which cement is injected into a fractured vertebra. While this treatment fixes the fracture and reduces pain, it does not restore the vertebra and person to their original height. Another problem with vertebroplasty, is that because the cement is injected as a liquid, it may leak outside of the vertebra, for example, through cracks in the vertebra. This may cause considerable bodily harm.
Viscous cement may reduce the risk of leakage, while sustaining an ability to infiltrate into the intravertebral cancellous bone (interdigitation) [see G Baroud et al, Injection biomechanics of bone cements used in vertebroplasty, Bio-Medical Materials and Engineering 00 (2004) 1-18]. In addition, viscous material may reduce the fracture. For example, PCT Application No. PCT/IL2006/000239 and IL Patent Application No. 174347 to Beyar et al. describe bone cements with certain formulations, commercially known as Confidence Bone Cement™, which provide an enhanced high-viscosity window of time during which the cement is suitably viscous for injection, fit using a designated delivery system and which are incorporated by reference herein. This type of bone cement rapidly achieves a high viscosity when its components are mixed and set slowly. The liquid phase is skipped during and immediately following the mixing of the components.
Another common treatment for fractured vertebras is kyphoplasty. This was first described in U.S. Pat. Nos. 5,108,404 and 4,969,888 to Scholten et al., wherein a fracture of a vertebra is taught to be reduced by first inflating a balloon inside the vertebra and thereby producing compaction of the cancellous bone to form a cavity. Bone cement is subsequently injected into the cavity after the balloon is withdrawn. The cement fills the cavity. In this procedure, because a lower pressure can be used to inject the cement, the problem of cement migration is reduced. However, this problem is not completely avoided.
U.S. Pat. Nos. 5,549,679 and 5,571,189 to Kuslich describe a device and method for stabilizing a spinal segment with an expandable, porous fabric implant for insertion into the interior of a reamed out disc which is packed with material to facilitate body fusion. U.S. application Ser. No. 10/440,036 of Kuslich et al. describes an improved method of correcting bone abnormalities by first accessing and boring into the damaged tissue or bone, and then reaming out the damaged and/or diseased area. Alternatively, the cancellous bone may be compacted by expanding a bag within the damaged bone. The bag may then be filled with fill material, such as a bone repair medium, thereby correcting and stabilizing the bony defect and deformity in a single step. This type of bag may be inflated with less fear of puncture and leakage of the inflation medium than a thin walled rubber balloon. Furthermore, this procedure provides the advantage of safely skipping the first balloon inflation steps of Scholten, by expanding the bag by introducing fill material, such as a bone repair medium and thereby correcting and stabilizing the bony defect and deformity in a single step. Nevertheless, this procedure is accomplished only by leaving the expanded bag inside the body organ after the injected material has solidified. Furthermore, when the bag is filled with inert filling materials, it is intentionally designed not to allow said material transfer through bag walls. U.S. patent application Ser. No. 10/949,217 to Lin et al. describes an extractable device for inserting a medicinal filling into a vertebral body. In this procedure, a filling member is made of a flexible and permeable wall. After the filling member is inserted into the spinal disc and/or vertebra, and a flowable medicine is injected and fully solidifies therein, closing threads are pulled to unlash the opening of a holding portion provided with the filling member. This enables the filling member to be extracted from the spinal disc to leave only the medicine in the spinal disc. Lin et al. do not describe a method or a device, specifically intended for compacting cancellous bone and/or promoting height restoration of the vertebral body. Further, Lin et al. discloses threads located on the distal end of the bag which are not for connecting the bag to other means.
It is the object of this invention to provide an improved method and apparatus that for treating a fractured vertebral body, and significantly lowering the risk of filler material leakage.